It is known to fabricate gas sensors based on resistive gas sensing, calorimetric gas sensing or Non Dispersive Infra-Red (NDIR) based gas sensing. Each of these sensors requires a heater.
In the resistive gas sensor, the heater heats the sensing material to a high temperature, at which the resistance of the material changes in presence of gas. In a calorimetric sensor, the heater heats a catalyst, and the temperature of the device increases in the presence of the target gas. In an NDIR sensor, a heater is used to provide Infrared radiation which is detected by an IR detector. The IR detector detects how much radiation has been absorbed by the target gas in the path between the emitter and detector to determine the gas concentration.
The heater used can either be a bulk device, such as a filament wire or in the case of NDIR sensors a micro-bulb. Alternately it can be fabricated on a semiconductor chip, for example as a micro-hotplate, where a heater is embedded within a dielectric membrane supported by a semiconductor substrate.
The biggest source of power consumption in these sensors is the use of the heater. As such different methods have been used to reduce the power consumption. One method used is to have a low power and a high power mode of operating the sensor. When the measured results indicate a low concentration of gas, the sensor operates in a low power mode, whereas when the results indicate a presence or high concentration of gas, then the sensor is operated in a high power mode (U.S. Pat. No. 5,255,556, EP2762881). An example different modes is to vary the frequency of measurement, for example having a high frequency of measurement during the high power mode, and having a low frequency of measurement during the low power mode. Changes in the pulse width of the measurement are also possible to achieve this.